1. Field of the Invention
The present invention relates to a circuit arrangement for a switch-mode power supply, wherein the switch-mode power supply has a primary side, which can be connected to a supply voltage, and a secondary side, which can be connected to a consumer, and wherein the circuit arrangement comprises a primary-sided switch, a control circuit for controlling the primary-sided switch and additional active primary-sided components. Furthermore, the invention under consideration also refers to a switch-mode power supply with such an active primary-sided circuit arrangement.
2. Description of the Related Art
Charging devices in the low power range are normally implemented as switch-mode power supplies today. Because of the compact design and low weight, these have gained acceptance in many application cases and are superseding the traditional linear devices. In spite of the advancing integration of separate circuit components, such as in the form of integrated circuits specific to the user (so-called ASICs, or Application Specific Integrated Circuits), for example, the electronics needed for a switch-mode power supply are still comparatively complex and the primary-sided circuit arrangement of a switch-mode power supply of that type consists of more than 20 separate circuit components.
FIG. 1, in the form of a wiring diagram, shows the circuit diagram of the primary side of a switch-mode power supply with primary regulation. The total of 24 components can be assigned here as follows: a converter-transformer 120, in which only the primary-sided winding 122 and the auxiliary winding 124 are depicted, 16 passive components, such as resistors, inductors and capacitors, and up to eight active components. The active components form the active primary-sided circuit arrangement of the switch-mode power supply and comprise four single diodes, which form a bridge rectifier 106, the switching transistor 102, an ASIC for pulse width modulation of the primary-sided switching transistor as control circuit 104 of the primary-sided switch 102, an auxiliary voltage diode 108 and a snubber diode 110.
In order to reduce the space requirements of the single components, there are currently various approaches, most of which are, however, not far-reaching enough and extend over only a few elements.
For example, in the area of the passive components, various resistors and even RC functions are integrated in one element array.
From the US American printed patent specification U.S. Pat. No. 6,134,123, it is furthermore known to accommodate the primary-sided switch and the control circuit for a switch-mode power supply on a common substrate and to produce it as a hybrid IC.
The solution disclosed in this publication, however, has the disadvantage that a major portion of the space-consuming elements, such as the rectifier or the auxiliary voltage and snubber diodes are still provided as external elements. Therefore, although this known solution achieves increased stability of the switch-mode power supply because of the spatial proximity of the control circuit and the primary-sided switch, no more extensive advantages are achieved with regard to miniaturization of a switch-mode power supply of that type.
Furthermore, from U.S. Pat. No. 5,355,301, a switch-mode power supply is known in which a printed converter is used. The active components, i.e., the bridge rectifier, primary-sided switch, control circuit and secondary diode are integrated in a single chip in this case and, assembled with the printed converter in a shared substrate. The contacting between this active chip and the voltage-converting area is accomplished via a further wiring layer. The contacting to the active chip is produced here via appropriate openings in the chip. The active element is consequently a constituent of a fully integrated switch-mode power supply and is not produced as a separate IC in its own IC housing.
The solution shown here therefore has, firstly, the disadvantage that the secondary diode that is also integrated does not make possible primary/secondary separation according to applicable standards. Furthermore, the technical solution of a fully integrated switch-mode power supply represents a very complex concept that can only be realized with high manufacturing costs.
In addition to the mentioned complexity of the components, the manufacture of the known switch-mode power supplies additionally requires complex logistics for the procurement of the single components and substantial investments in pick-and-place machines and testing technology for the manufacture.